It is well known from the old days that as the development of photographic silver halide photosensitive material (often simply referred to as photosensitive material, hereinafter) is repeated, silver deposits and accumulates on developing equipment including tanks or vats, and developing tank walls, racks and rollers of automatic processors. Such silver deposit is also known as silver contaminant or sludge. Since silver sludge, if left as such, can adhere to a photosensitive material to stain its image, periodic washing and maintenance of the developing equipment is necessary.
There is an increasing demand for quick processing in the development of photographic silver halide photosensitive material. The feasibility of quick processing is enhanced by increasing the activity of developer on one hand, but is largely governed by the nature of photosensitive material. Automatic developing machines or processors generally involve development, fixation, washing and drying steps, and among others, the drying step is a key for quick processing. In order to complete drying as fast as possible, it is most effective to reduce the silver quantity of photosensitive material.
Since plate-shaped silver halide grains have a high covering power, the silver quantity can be reduced without impairing photographic properties and image quality. A reduced silver quantity is advantageous not only for the drying step, but also for quickening development, fixation and washing steps. Therefore, the use of plate-shaped silver halide grains is most suitable for quick processing. The nature of plate-shaped silver halide grains is described in Research Disclosure, Vol. 225, Item 22534, pages 20-58 (January 1983), Japanese Patent Application Kokai (JP-A) Nos. 127921/1983 and 113926/1983, and U.S. Pat. No. 4,425,425.
Nevertheless, since the plate-shaped silver halide grains have an extremely larger surface area than conventional potato like grains, more silver halide is dissolved out to deposit more silver sludge during development than with the potato like grains. Then the advantage of plate-shaped silver halide grains for quick processing is not utilized to a full extent.
In some less sensitive photosensitive materials, such as printing photosensitive materials which need not have high sensitivity in nature and laser printer photosensitive materials which need not have high sensitivity by virtue of systematic electronic cooperation, silver halide grains are used having a smaller size and readily soluble silver bromide or chloride rather than silver iodide so that silver sludging is more likely to occur, although this construction can accommodate quick development irrespective of single side photosensitive material. The silver sludge problem is serious with industrial X-ray photosensitive materials since they bear an amount of silver coated nearly three times the silver coating amount of medical X-ray photosensitive materials and the silver halide grains used are of smaller size.
Further, silver sludge is also a serious problem in the processing of versatile picture-taking negative photo-sensitive materials since the sulfite concentration of the developer is increased and the developing time is made rather longer in order for solution physical development phenomenon to make a larger contribution to the graininess of images.
As mentioned above, the silver sludge problem is inevitable and has been left unsolved in all types of photo-sensitive material processing systems.
The environmental problem is also of greater concern these days. The disposal of used developer is not an exception. For environmental protection, it is very important and desirable to reduce the amount of replenisher as well as the amount of used developer. However, if the amount of replenisher is reduced, the concentration of silver dissolved into the developer is increased in counter proportion thereto, resulting in more silver sludge. The amount of used developer can be reduced often at the sacrifice of photographic capability because optimum control of the automatic processor is cumbersome. With these problems, it is not easy at present to reduce the amount of replenisher.
Washing to remove silver sludge is generally carried out by emptying the developing tank of the developer, filling the tank with a solution of a strong oxidizing agent such as cerium sulfate, and holding the oxidizing solution in the tank for about ten minutes to about 30 minutes or longer with stirring. Then the developing tank should be thoroughly washed with water because a trace of the oxidizing agent, if left in the developing tank, would oxidize and deteriorate the developer. This washing operation is one of the daily maintenance burdens of an automatic processor. Therefore, it is desired to overcome the problem in view of the safety of operation and the additional pollution by the washing solution.
One approach for reducing silver sludge is by adding a mercapto compound as an antisludging agent for decreasing silver ions dissolving in a developer and/or suppressing reduction of silver ions to silver as disclosed in JP-A 24347/1981 (JP-B 4702/1987). The mercapto compound used is a mercaptobenzimidazole compound having a sulfonic acid group or a salt thereof as a water soluble group.
This approach is accompanied by an inevitable function of suppressing development itself with the attendant drawback of sensitivity lowering. Since photosensitive materials have different sensitivity to the mercapto compound, no consistent effect is achieved simply by adding a fixed amount of the mercapto compound. The sensitivity lowering is a serious drawback in the photosensitive material developing system which is designed for processing with as high sensitivity as possible. A variation in gradation is also a problem to be avoided.